An eFuse is a technology which allows for the dynamic real-time reprogramming of computer chips. By utilizing a set of eFuses, a chip manufacturer can allow for the circuits on a chip to change while it is in operation. The primary application of this technology is to provide in-chip performance tuning. For example, if certain sub-systems fail, or are taking too long to respond, or are consuming too much power, the chip can instantly change its behavior by “blowing”, or programming, an eFuse.
By design, e-Fuses are sensitive to large currents and voltages, e.g., 1.5V for 100 ns. For example, by forcing a large current through the eFuse, it can be blown or programmed; breaking the eFuse structure resulting in an electrical open. During an ESD event, the voltage on the supply can increase to a high level of several volts. Since the supply voltage of the control circuit and the circuitry generating the program enable signal is not actively powered during the ESD event, the outputs of these circuits can be in an undefined state during the ESD event. This may create conditions for unwanted eFuse programming. As a result, with currently used eFuses, there is a risk that the eFuses are programmed by high voltages and currents that can occur during an undesirable ESD event.
More specifically, during a negative pulse on the supply rail of the eFuse circuit (referred to as Vf source), an ESD current will primarily go through the ESD device, however, some current will also pass through the parasitic body/drain diode of a current source NFET. As should be recognized, the current source of the NFET is used to drive current through the eFuse when programming the eFuse, but the negative pulse through the body/drain diode of a current source NFET during the ESD event can also go through the eFuse. This current might damage the un-programmed eFuse.